1. Field of the Invention
The present invention relates to a universal sphygmomanometer simulator for live training and evaluation.
2. Background Information
Sphygmomanometer
Blood pressure refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs of a patient or subject (human or animal). The pressure of the circulating blood decreases as blood moves through arteries, arterioles, capillaries and veins; the term blood pressure generally refers to arterial blood pressure, i.e., the pressure in the larger arteries, arteries being the blood vessels which take blood away from the heart. Blood pressure in humans is most commonly measured via a device called a sphygmomanometer, which traditionally uses the height of a column of mercury to reflect the circulating pressure. Although many modern blood pressure devices no longer use mercury, blood pressure values are still universally reported in millimeters of mercury.
A sphygmomanometer or blood pressure meter (also commonly referred to as a sphygmometer) is composed of an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.
The word “sphygmomanometer” comes from the Greek “sphygmós” meaning “pulse and the scientific term “manometer” meaning “pressure meter”. The invention of the sphygmomanometer is commonly attributed to Samuel Siegfried Karl Ritter von Basch in 1881. Scipione Riva-Rocci is attributed with introducing a more easily used version in 1896. While in 1901, Harvey Cushing modernized the device and popularized it within the medical community.
A conventional sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically. The usual unit of measurement of blood pressure is millimeters of mercury (mmHg) as measured directly by a manual sphygmomanometer.
There are two categories of sphygmomanometers: manual sphygmomanometers and digital sphygmomanometers.
Manual sphygmomanometers require a stethoscope for auscultation. They are used by trained practitioners, and cannot be used in environments too noisy to permit hearing the characteristic sounds. It is possible to obtain a basic reading through palpation, but this only yields the systolic pressure. Mercury sphygmomanometers are often considered to be the gold standard for manual sphygmomanometers and measure blood pressure directly by observing the height of a column of mercury; errors of calibration cannot occur (unless the markings on the scale of millimeters are wrong). Due to their accuracy, mercury sphygmomanometers are often required in clinical trials of pharmaceuticals and for clinical evaluations of determining blood pressure for high-risk patients including pregnant women. Aneroid sphygmomanometers (mechanical types with a dial) are manual sphygmomanometers that are in common use, and can require regular calibration checks, unlike mercury manometers. Aneroid sphygmomanometers are considered safer than mercury based, although possibly less accurate. A major cause of departure from calibration is mechanical jarring. Aneroid sphygmomanometers mounted on walls or stands are less susceptible to this particular problem.
Digital sphygmomanometers typically use oscillometric measurements and electronic calculation rather than auscultation. They may use manual or automatic inflation. These are electronic, and claimed to be easy to operate without training by anybody, and can be used in noisy environments. They measure systolic and diastolic pressures by oscillometric detection, using a piezoelectric pressure sensor and electronic components including a microprocessor. They do not measure systolic and diastolic pressures directly, but calculate them from the mean pressure and empirical oscillometric parameters. Digital oscillometric monitors are also confronted with “special conditions” for which they are not designed to be used: arteriosclerosis; arrhythmia; preeclampsia; pulsus alternans; and pulsus paradoxus. The oscillometric method of detection used gives blood pressure readings that differ from those determined by auscultation, and vary subject to many factors, for example pulse pressure, heart rate and arterial stiffness. In addition to the digital oscillometric monitors drawbacks where they cannot be used, the overall accuracy of such devices has been questioned.
As a note the category of digital sphygmomanometers is defined by the method of calculating the resulting pressure rather than the type of display. A manual sphygmomanometers using auscultation may have a digital display of the associated pressure.
As shown in FIG. 1A, in humans, the cuff 16 of a typical manual sphygmomanometer 10 is normally placed by the medical professional smoothly and snugly around an upper arm 12 of a patient 14, at roughly the same vertical height as the heart while the patient is seated with the arm 12 supported. It is essential that the correct size of cuff 16, typically adjustable within a given range, is selected for the patient 14. Too small a cuff 16 results in too high a pressure, while too large a cuff 16 results in too low a pressure. For clinical measurements it is usual to measure and record blood pressure measurements of both arms of the patient 14 in the same consultation to determine if the pressure is significantly higher in one arm than the other. The cuff 16 is inflated, such as via bulb 22, until the artery 18 is completely occluded.
With the cuff 16 inflated until the artery 18 is completely occluded, a stethoscope 20 is placed in a position to listen to sounds (Korotkoff sounds) through the brachial artery 18, then medical professional slowly releases the pressure in the cuff 16 via releasing manual valve 24. As the pressure in the cuffs 16 falls, a “whooshing” or pounding sound is heard when blood flow first starts again in the artery 18. The pressure, shown on display or gauge 28, at which this sound began is noted and recorded as the systolic blood pressure 26. The cuff 16 pressure is further released until the sound can no longer be heard. The pressure reading on display 28 when the sound can no longer be heard is recorded as the diastolic blood pressure 30. In noisy environments where auscultation is impossible (such as the scenes often encountered in emergency medicine), systolic blood pressure 26 alone may be read by releasing the pressure until a radial pulse is palpated.
The sounds that medical professionals listen for when they are taking blood pressure using a manual sphygmomanometer are known as Korotkoff sounds and are named after Dr. Nikolai Korotkoff, a Russian physician who described them in 1905, when he was working at the Imperial Medical Academy in St. Petersburg.
If a stethoscope 20 is placed over the brachial artery 18 in a normal person (without arterial disease), no sound should be audible. As the heartbeats, these pulses are transmitted smoothly via laminar (non-turbulent) blood flow throughout the arteries, and no sound is produced. Similarly, if the cuff 16 of a manual sphygmomanometer 10 is placed around a patient's upper arm 12 and inflated to a pressure above the patient's systolic blood pressure 26, there will be no sound audible via a stethoscope 20 placed over the brachial artery 16. This is because the pressure in the cuff 16 is high enough such that it completely occludes the blood flow. This is similar to a flexible tube or pipe with fluid in it that is being pinched shut.
If the pressure is dropped to a level equal to that of the patient's systolic blood pressure 26, the first Korotkoff sound 32 in FIG. 10 will be heard. As the pressure in the cuff 16 is the same as the pressure produced by the heart, some blood will be able to pass through the upper arm 12 when the pressure in the artery 18 rises during systole. This blood flows in spurts as the pressure in the artery 18 rises above the pressure in the cuff 16 and then drops back down beyond the cuffed region, resulting in turbulence that produces an audible sound 32. As the pressure in the cuff 16 is allowed to fall further, thumping sounds continue to be heard as long as the pressure in the cuff 16 is between the systolic 26 and diastolic 30 pressures, as the arterial pressure keeps on rising above and dropping back below the pressure in the cuff 16. Eventually, as the pressure in the cuff 16 drops further, the sounds change in quality, then become muted, and finally disappear altogether. This occurs because, as the pressure in the cuff 16 drops below the diastolic blood pressure 30, the cuff 16 no longer provides any restriction to blood flow allowing the blood flow to become smooth again with no turbulence and thus produce no further audible sound.
There are five Korotkoff sounds that are described. The first Korotkoff sound 32 is the snapping sound first heard at the systolic pressure. Clear tapping, repetitive sounds for at least two consecutive beats is generally considered to occur at the systolic pressure 26. The second Korotkoff sounds 34 are the murmurs heard for most of the area between the systolic 26 and diastolic 30 pressures. The third Korotkoff sound 36 is described as a loud, crisp tapping sound. The fourth Korotkoff sound 38, at pressures within 10 mmHg above the diastolic blood pressure 30, was described as “thumping” and “muting”. The fifth Korotkoff sound 40 is silence as the cuff 16 pressure drops below the diastolic blood pressure 30. The disappearance of sound is considered to occur at the diastolic blood pressure 30, actually about 2 mmHg below the last sound heard.
In addition to the Korotkoff sound heard through the stethoscope 20 in operation of a manual sphygmomanometer 10 the needle or gauge 28 of a manual sphygmomanometer 10 shows a slight “bump” as the blood rushes through the artery 18 causing a slightly elevated pressure reading. This visually noticeable bump in the pressure display occurs just before the first Korotkoff sound 32 and continues at pressures below the fifth Korotkoff sound 40. These visible gauge bumps are referenced herein as Korotkoff gauge bumps merely for the purpose of having a uniform reference for these features. Visualizing and recognizing the Korotkoff gauge bumps are also an important aspect of manual sphygmomanometer training.
Training
With the above described background it is important to have a method of accurately training medical professionals to accurately take blood pressure readings of patients using manual sphygmomanometer.
A number of blood pressure medical simulators have been developed to assist training medical professionals to accurately take blood pressure readings of patients using manual sphygmomanometer. For example see the LIFE/FORM® Blood pressure simulator using a manikin arm through which fluid is supplied at the desired pressure. Similarly Gaumard supplies a S415 BLOOD PRESSURE TRAINING SYSTEM™ which includes a full-size adult left arm that may also be attached to any Gaumard adult manikin and which is programmable to the desired simulated blood pressure. Laerdal also manufactures a BLOOD PRESSURE TRAINING ARM™ that provides “a lifelike, adult arm with an electronic trainer” designed for training the procedure of blood pressure measurement using a manual sphygmomanometer. Similarly, Armstrong Medical Industries manufactures a BLOOD PRESSURE SIMULATOR in the form of a manikin arm type device which is described as “a lifelike simulator” that “allows the presetting of values for both systolic and diastolic pressures. It provides an excellent means to practice listening to and distinguishing blood pressure sounds prior to actual clinical experience. It is possible to audibly discern the five Korotkoff phases. The electronically generated sounds are digitally recorded.” While these simulators provide effective tools for supplying the trainees with a wide range of blood pressures to obtain and provide a method of verifying the accuracy of the trainee's results, they do not provide the real live aspects of interacting with a human regardless of how “lifelike” the systems become.
In recognizing the drawbacks of existing manikin based simulators educators will often have trainees work on trial subjects, most commonly by pairing the trainees together in which they switch from being the trainee and patient. This training has the advantage of introducing live subjects with all the aspects and nuances of interacting with live subjects that remains difficult to capture with manikin type simulators. However this training technique offers very little variation in the blood pressures that the trainees will experience (in general the class room subjects have an average blood pressure) and does not allow the teacher to easily verify the results of a particular trainee or to present a trainee with a desired blood pressure to measure.
Another medical training approach used in medical training is using live actors as patients who are reporting a selections of symptoms associated with a given malady or condition. In such training exercises the trainees are told to measure the actor/patient's blood pressure (which is often not indicative of an actor's simulated condition), and then told to ignore the results and assume that the trainee recorded results then given to the trainee and more in line with the actor's simulated condition. This live training technique also has the advantage of having trainees work with live subjects with all the aspects and nuances of interacting with live subjects, but it does not allow the trainee to actually obtain abnormal pressures (barring an actual abnormal condition of the actor) and lessens the realism of the training event as the trainee must disregard the obtained values and imagine some other imaginary set of values. This method also fails to allow the trainer to validate the accuracy of an abnormal blood pressure measurement obtained by the trainee.
There remains a need in the art to effectively expand the useful tools applicable to medical teachers and to provide effective tools for use with live subjects that supply the trainees of manual sphygmomanometer with a wide range of blood pressures to obtain and provide a system of verifying the accuracy of the trainee's results.